I think my 0331 is cracked too although it still drives good, it uses coolant and the oil cap on the valve cover is milky. My Crown Vic cap is clean, so I am worried. Is the 0630, the best head to get for replacement? I've seen heads for as low as $50 around here on Craigslist. What years had the 0630?
As far as that aftermarket aluminum head goes, I would never put an aluminum head on a cast iron block. Escorts always had an issue with it and manufacturers had to develop special gaskets and weird surface finishes for the mating surfaces to make them work. We did the prototype machinings for the Ford modular engines and 3.8/4.2's when they went to aluminum heads and surface finishes were critical (computerized profilometer, etc.) It should be intuitive that you want the block and head to expand from heat at the same rate if you have a critical sealing surface between them. Yes, you can seal between aluminum and iron, but why? If you want aluminum, get an aluminum block too.